With large-scale development of information technologies, an SSD comes into being. An SSD using a Flash medium features high performance and low power consumption, and can greatly reduce a delay of a storage system. The SSD has higher reliability because the SSD does not need a mechanical structure.
As a storage medium of an SSD, a NAND flash has limited erasing times. This is a key factor affecting a service life and performance of the SSD. In the NAND flash, data is organized in a form of a NAND flash physical block and a NAND flash physical page. One NAND flash physical block includes several NAND flash physical pages. A NAND flash physical block is a smallest unit for performing an erase operation, and a NAND flash physical page is a smallest unit for performing a write/read operation. After data is written to a NAND flash physical page, data can be written to the NAND flash physical page again only after an erase operation is performed on a NAND flash physical block in which the NAND flash physical page is located. A NAND flash physical page includes several storage units, and data is stored in a storage unit of the NAND flash in a form of a charge in a floating gate. Erasing performed on a storage unit reduces insulativity of an insulation layer between the floating gate and a channel. After a quantity of erasing times, an electron cannot be maintained in the floating gate for an enough time. Consequently, a large quantity of bit errors are produced in stored data. If an error correction capability of an SSD controller is exceeded, it is considered that a corresponding NAND flash physical page/physical block is already damaged.
Reducing an amount of data actually written to a NAND flash medium is a key factor for improving a service life of an SSD. In an actual application, data written to an SSD is spatially correlated. A method in which data is compressed before being written to a NAND flash is proposed to reduce an amount of actually written data. However, in other approaches, error checking and correction (ECC) logic of an SSD controller needs to support multiple code rates. Consequently, it is highly complex to implement the ECC logic, a software management algorithm is complex, and service lives of different physical pages in a physical block of the NAND flash are different.